just a quick n00b question:
can i just leave the stuff i dont want to sell but dont need right then in like a cupboard or chest of draws and come back to it later? Will it stay there indeffinitely or dissapear when i leave the town/area/whatever?

Can't say for sure as I don't tend to do that, but I'm pretty sure you can. At the very least in your quarters in the Brotherhood of Steel bunker. (Once you get in anyway) Can't remember if it's on level 2 or 3 though.

I recommend loading it into an NPC.

What if the NPC dies??

I believe corpses disappear after you leave an area. I would not allow my npcs to die if at all possible.

I've noticed other things I haven't looted stay at their place seemingly indefinitely. So I guess it works, but I actually wondered about the same thing and therefore refrained from doing it. But I also stored my items in my locker in the Brotherhood and it was all still in it when I came back.
Corpses don't just vanish, they rot. After a while there is nothing left but a skeleton, and then some time later the corpse totally disappears, but seemingly anything it had on it will be left on the ground. At least it happend this way in the raider base I, eh, raided towards the beginning of the game, and some other enemies :)
So, I am not entirely sure about this, but it seems like no item just disappears, no matter where you left it (Unless you drop it in a random encounter or another place you can't come back to, of course).

I didn't see any skeletons after finishing off the raider base, I would leave and come back, and their corpses would be gone and only a puddle of blood and armor setting there.

You'll never be able to hold more than a small fraction of what your buddy NPC's are holding if they die, due to weight limits.

in both fallout 1 and 2, you can leave loot wherever you want and it will still be there when you get back. loot from dead bodies will still be there if you do not pick it up, just like weclock says. the only time you cannot get loot from dead bodies is if you burn/vaporize the body in the killing blow (e.g., using a flamer).
i've used bookshelves/lockers throughout both games to keep tons of loot all over the map. no one will ever take it, and no one will ever take loot left on the ground, either.

Yeah keep all your loot in a memorable locker or something, somewhere that you won't forget, it won't disappear

In Fallout 1, I used my NPCs to carry tons of gear (I mean literally multiples of 2,000 pounds). Whenever they died in combat, I would just re-load and re-start. But that's just me. I always saved right before any big battles, so I managed to get all four of my NPCs all the way through the game.
But using random lockers and what-not works too. Probably best to pick one centrally located that's near a merchant you trade with. You can leave stuff lying on the ground, but it's difficult to sort through it and feels lame.
In Fallout 2, the trunk of the car is your best friend.